The present invention relates to a magnetic barrier paper useful for protecting magnetic disks and various electronic components from the deleterious effects of stray magnetic fields.
As the use of electronics has become more widespread, and systems incorporating electronics have become more sophisticated, a phenomenon known as electronic magnetic interference ("EMI") has become a major problem to the use of such electronic systems. EMI is an electrical phenomenon that causes an undesired result at a receiving device. It is generated most often by man-made electrical components but can also be generated from natural sources such as lightning or simple triboelectric discharges. EMI can be manifested as interference that is conducted into or out of electronic equipment, or as interference that is radiated into or out of the circuitry thereof.
The effect of EMI can be as serious as a "shut down" of a computer because of memory loss. In its less serious aspects, EMI can result in phenomena such as the annoying hum heard on poorly designed stereo systems. The FCC is enforcing regulations on equipment that generates EMI signals at higher frequencies (FCC part 15, docket 20780, for example). Some of the more common systems which contribute to or are affected by EMI are power switching supplies, electronic games, electronic watches, calculators, microwave ovens, computers (both personal and industrial), stereos, televisions, and electronic components.
Stray magnetic fields are particularly injurious to an article finding increasingly widespread use, namely, the conventional 5" floppy disk for computers. This disk stores information on its surface by having a magnetic code imprinted in the coating formed thereon. Stray magnetic fields can erase or destroy the information encoded in this coating, resulting in an irretrievable loss of work product.
Conventional magnetic record disk assemblies comprise an outer jacket permanently encasing the disk itself. The jacket has a central opening aligned with the opening in the disk, to permit access by a drive mandrel in the disk drive unit. The jacket also has a radially extending oblong opening for receiving a reading and writing head of the data processing unit. U.S. Pat. No. 4,038,693 in the name of Huffine et al discloses such a disk assembly in which the jacket is formed from an antistatic material. This prevents static electricity from accumulating on the jacket during handling, and thus prevents extraneous signals from being sent to the transducer associated with the reading and writing head. The jacket comprises an outer layer of electrically insulating material and an inner layer of an electrically conductive material, provided for the purpose of draining away any electrostatic charge which accumulates on the outer layer.
It is also known to produce paper having magnetic properties. U.S. Pat. No. 4,234,378 to Iwasaki et al teaches such a paper, containing 70-90 parts by weight magnetoplumbite barium ferrite powder and/or magnetoplumbite strontium ferrite powder, the particles of which have a primary particle size of about 0.1-2 microns and a secondary particle size smaller than about 20 microns, 1-10 parts by weight anionic synthetic latex and/or synthetic resin, about 2-10 weight percent cationic organic polymer electrolyte and more than about 5 parts by weight pulp fibers. The sheet is formed by conventional paper making techniques, and is thereafter magnetized.